Modern pressurized passenger aircraft fly at altitudes in the range of 18,000 to 40,000 feet. At these altitudes the air is at a reduced density because the atmospheric pressure is much lower than at sea level. Thus, the partial pressure of oxygen in the air is not sufficient to sustain normal respiration. Consequently, there has been a need for a system to supply additional oxygen for the survival of passengers in the event of a depressurization emergency of the airplane cabin.
In the prior art, especially in U.S. Pat. Nos. 4,098,271 and 4,832,017, there are shown emergency oxygen breathing apparatuses which each include a facepiece having valves, the facepiece designed to cover the nose and mouth and also is connected to an oxygen delivery tube. Connected between the facepiece and the delivery tube is a bag which functions as a reservoir, permitting an efficient use of the limited oxygen supply. In order to activate the flow of oxygen, the facepiece and bag assembly must be pulled down by the passenger; current specifications require that the assembly be capable of withstanding a static tensile force of not less than 20 pounds for at least three seconds. In accordance with FAA requirements, these bags are made of a lightweight and resilient vinyl plastic material. However, such prior art bags in their current design cannot themselves withstand the 20 pound static tensile force without failure. The solution found in prior art systems is to insert within the bags a strain relief mechanism, typically a taut string, to withstand the tensile force.
FIG. 1 shows such a prior art system. This prior art (indicated generally at 10) includes a facepiece 11, bag 12, and a delivery tube 13. The assembly is provided with a string 14, connected from the facepiece directly to the delivery tube in which the string functions as a strain relief mechanism. This strain relief mechanism is designed to withstand the 20 pound static tensile force that would otherwise be applied to the bag. However, such prior art devices are difficult to manufacture and include extra materials and process steps resulting in additional time needed for the manufacture of the device, thus contributing to the expense. The prior art connectors joining the bag and facepiece are difficult to assemble and could not easily be assembled by maintenance personnel in the field. Further, the prior art connectors cannot withstand the 20 pound static tensile force without a strain relief mechanism. As a result, it would be desirable to eliminate the string 14 from the assembly.
One solution would be to select stronger materials which would produce an inherently stronger bag. However, other materials that could be used may be more flammable or entail increased weight and, therefore, cost. Consequently, such materials would need to undergo the long and costly process of being "requalified" in order to conform to FAA requirements. Therefore, it is not practical to use stronger bag materials as a substitute for the strain relief mechanism. Additionally, the prior art joint between the bag and the facepiece is not sufficient to withstand the required load.